This invention relates to the field of surgical instruments, and more particularly to surgical guiding instruments used in orthopedic surgery, particularly hip arthroplastic surgery, for determining an appropriate resection line through a bone.
Artificial hip joints include several components. A femoral component of a hip prosthesis comprises an elongate stem or shaft at its distal end that is affixed within the medullary canal of the femur. A proximal end of the stem includes a neck region, to which is attached a femoral head. The acetabular shell is a separate component of an artificial hip joint that is affixed within existing bone such as the acetabulum. The acetabular shell includes a cup-like region that receives the femoral head. The femoral head and the acetabular shell form an articulation couple and smooth, low frictional movement of the femoral head within the shell is essential to ensure proper functioning of the artificial hip joint. Proper positioning of the artificial hip joint is also important to proper functioning of the artificial hip joint.
Hip arthroplasty is a surgical procedure in which a natural hip joint is removed and replaced with an artificial joint. During such a surgical procedure, a diseased portion of the femur is excised, usually by cutting along a portion of the femoral neck. A prosthetic femoral component and a prosthetic femoral head replace the natural structures that are surgically removed. The positioning of the femoral component of the prosthesis is important to ensure proper fit and smooth rotation of the femoral head within its socket (i.e., the acetabular shell).
The size of the femoral prosthesis, particularly the length of the neck portion and the size of the femoral head, all vary with a patient's anatomy. For maximum success and patient comfort, orthopedic implants must simulate as closely as possible the patient's anatomy, including bone length, size, and placement within the body relative to other bones and organs. Misplacement of the implant within the bone can cause significant trauma in the surrounding bone, muscles, tendons and ligaments and can disable the patient.
It is therefore necessary to ensure that orthopedic implant structures are properly placed within a patient. In the case of a hip joint prosthesis, it is important that the anatomic center of rotation of the femoral head within the acetabular shell be located and maintained during the implantation of the replacement structure. Misplacement of the center of rotation during implantation of the femoral component of the hip joint prosthesis can affect the patient's leg length and cause potentially irreversible damage and extreme trauma to weight-bearing joints.
Femoral resection procedures involve the resection, or excision, of at least the diseased portion of the femur, typically the femoral head, by cutting at some location along the femoral neck. Difficulty arises when the resection location is determined without regard to the size of the femoral component of the hip joint prosthesis. An incorrect neck resection location can cause the prosthesis to fit improperly within the medullary canal of the femur and/or can result in misplacement of the prosthetic center of rotation relative to the anatomic center of rotation of the femur.
In current surgical techniques, the location of the resection is not rigidly instrumented to coordinate with the prosthesis to be implanted. This is a disadvantage and can adversely affect the ability to reestablish the normal anatomic center of rotation of the femoral head. Due to the fixed geometric relationship of the collar of the prosthesis to the head center, the location of the resection will ultimately determine the location of the center of rotation. Thus, with no instrumented means to control the location of the resection, it may be difficult to accurately restore the center of rotation of the femoral head.
Accordingly, there is a need for surgical instruments that will assist surgeons to resect the femoral neck at the appropriate location to reproduce within the artificial joint the hip's anatomic center of rotation.
It is therefore an object of the invention to provide an apparatus for determining the proper femoral neck resection line during hip replacement surgery. It is another object of the invention to provide improved methods of performing surgical femoral resections. A further object is to provide an apparatus that enables surgeons to accurately reproduce the center or rotation of a femoral head during hip replacement surgery. These and other objects will be apparent from the description that follows.